First long term study on medical cannabis shows only small adverse effects, but also small reductions in pain

A new study conducted on the medical consumption of cannabis came up with some good news, and some bad news: for starters, while there were some adverse effects on consumers, no serious effects were reported. However, the reduction in pain also seems to be very small.

Image via Wiki Commons.

Dr. Mark Ware, Associate Professor in Family Medicine and Anesthesia at McGill University has conducted the first ever long term study on the effects of Medical Cannabis; he studied 216 individuals with chronic pain, and 215 controls (chronic pain but no current cannabis use) from seven clinics across Canada. Several randomized controlled trials of smoked cannabis have shown efficacy in chronic pain and spasticity, but these trials have been short (1-3 weeks of exposure) with small sample sizes (20-60 subjects).

“We conducted a prospective cohort study to describe safety issues among subjects with chronic noncancer pain. A standardized herbal cannabis product (12.5% THC) was dispensed to eligible subjects for a one-year period; controls were subjects with chronic pain from the same clinics who were not cannabis users. The primary outcome consisted of serious adverse events (SAEs) and non-serious adverse events (AEs).”

The study evaluated the safety of cannabis use by patients with chronic pain over one year. They found that there was a significant difference in the rate of non-serious adverse effects at a rate of 2.5g herbal cannabis per day. These non-serious disorders included nervous system disorders, respiratory disorders, infections and psychiatric disorders. Twenty-eight (13%) subjects in the cannabis group reported at least 1 SAE, compared with 42 (19%) in the control group.

The main non-serious affection was respiratory. The researchers write:

“We found 78 respiratory events in the cannabis group and 56 in the control group, and most were considered mild or moderate. No increase in risk of serious respiratory AE associated with medical cannabis use was detected. Medical cannabis users had a higher rate of developing non-serious respiratory AEs during one year of follow-up compared to controls. This is consistent with reports that long-term cannabis smoking is associated with an increased risk of chronic bronchitis.”

But on the other side, while the reduction in pain was statistically significant, it was significantly lower than expected – comparable to a placebo effect (a placebo mirror was not conducted).

Image credits: Ware et al, 2015.

It should be kept in mind that this doesn’t affect the debate on the recreational legalization of cannabis, but such a minor improvement in subjective pain estimates doesn’t really speak strongly about its pain-killing abilities.